Radiotherapy and chemotherapy, alone or combined together with surgery, are essential therapeutic arsenals against human cancer. The association between chemotherapy and radiotherapy was widely used in cancer treatment. Although still not completely elucidated, the biological basis of action of the cytotoxics relies on cellular mechanisms, such as cell cycle or DNA damage, which is also important for the radio-induced cell death, leading to the additive or even better synergistic benefits by combining different treatments in cancer therapies.
Recent progress in developing biological drugs (monoclonal antibodies, cytokines/kinase inhibitors, immunotherapies/vaccines) has proven their efficiency and specificity towards a subset of tumors. But they are often used in combination with chemical cytotoxics. Despite of many progresses in the development of new cytotoxic drugs, the drug resistance to chemotherapy is still a major clinical concern in the treatment of cancers. The understanding of the mechanism of drug resistance related to drug uptake/efflux, metabolic degradation, mutagenesis of target, enhanced repair, signaling of cell death (apoptosis and necrosis) is essential for ensuring efficiency of chemotherapy and improving therapeutic index, especially, in some treatment-resistant tumors.
In the last decade, many investigations were carried out in this field, and the complexity of signal transduction in response to radiation began to be delineated. In this respect, genes of particular interest to be targeted with ionizing radiations are those involved in the regulation of radiation-induced lethality mechanisms, such as apoptosis or DNA repair. As double-stranded breaks (DSBs) are the most lethal DNA damages, the efficacy of ionizing radiation decreases as that of DSB repair increases.
Two mechanisms are involved in the repair of DSBs: non homologous end-joining (NHEJ, sequence-independent pathway) and homologous recombination (HR, sequence-dependent pathway) (reviewed by Jackson, 2002). Targeting genes involved in these two main DSB repair pathways has so far led to little or moderate radio-sensitivity, depending on the used approaches and cancer cell lines (Belenkov et al., 2002; Marangoni et al. 2000a; Ohnishi et al, 1998).
Ku (e.g., Ku70 and Ku80) and DNA-PKcs proteins are important in the repair of radiation- or chemo-induced DNA DSBs. If damage cannot be repaired on time, cells die. Therefore, they represent potentially interesting molecular targets for sensitizing target cells and tissues to radiotherapy and chemotherapy. Many approaches have thus been conceived and carried out to try to inhibit these key proteins (Ku70/Ku80, DNA-PKcs, etc.) involved in the NHEJ pathway, which is predominant in mammalian cells:
1) Inhibitors of P13K (phosphatidylinositol-3-kinase) (i.e., DNA-PKcs, ATM, ATR) (Bouton et al., 2000; Durant & Karran, 2003; Willmore et al., 2004; Vauger et al., 2004);
2) Negative dominant & peptides (C-terminal of KU80) (Marangoni et al., 2000b; Kim et al., 2002);
3) Single chain antibody variable fragment (scFv) (DNA-PKcs) (Li et al. 2003a);
4) RNA Aptamer (SELEX: RNA binding Ku) (Yoo & Dynan, 1998);
5) Antisense (Ku70,Ku80, DNA-PKcs) (Li et al., 2003b; Marangoni et al., 2000c; Sak et al., 2002);
6) siRNA (DNA-PKcs) (Peng et al. 2000).
Despite these tremendous efforts, the combination of the targeting of genes involved in DNA repair pathways and cancer therapies is still in early experimental stages and no clinical study has shown any proven benefits so far. It is worth to note that the above described approaches share a common feature: they target a single effector (protein) involved in a complex cascade pathway (such as NHEJ) with possible bypass or compensation.
The patent application WO2005/040378 disclosed compositions and methods of interfering with DNA double strand break repair pathways in mammalian cells. Particularly, it relates to nucleic acid molecules that interfere, in a non gene-specific manner, with DNA damage sensing, signaling and/or repair pathways, as well as to their uses for triggering cell lethality of tumors submitted to anticancer therapies. It describes that the sensitivity of cells to direct or indirect DNA damaging therapies can be enhanced by using (chemically modified or not) short dsDNA molecules which act as mimics of broken DNA fragments and are recognized as DSB sites induced by the DNA damaging treatments (i.e. the substrate mimics of DSB). These molecules, also designated by the name of “DSB bait” molecules (Dbait in short), confer or increase sensitivity of any tumor cell to DNA damaging cancer therapy treatment, namely chemotherapy and radiotherapy. Dbait molecules act by baiting and hijacking the holocomplex of DNA DSB repair enzymes, and thereby interfere with DNA lesion sensing, signaling and/or repair processes. Accordingly, this application relates to Dbait molecules in combination with physical and/or chemical agent(s) which can directly or indirectly cause DSBs of DNA.